C-keywords, identifiers, comments

Keywords: the C language provides a special meaning of the symbol, also known as a reserved word.

A 32 keyword in C, these keywords are given special meanings, they must never be used as variable names or function names.

Auto Double int struct break else long switch

Case enum Register typedef char extern return Union

const float Short unsigned continue for signed void

Default goto sizeof volatile do if and static

Characteristics of keywords

1 are all lowercase

2> displays special colors in the development tool or in the Smart Text Editing tool. By default, all keywords in the C language are shown in Xcode with a violet-brown

Two. Identifiers

Identifiers are some of the symbols and names that you customize in your program. To differentiate from keywords: the keyword is the symbol that is provided by the C language by default, and the identifier is customized by the programmer.

the role of identifiers

(1) An identifier, literally understood, is a symbol used to identify something, the purpose of which is to separate it.

(2) In fact, the function of the identifier is similar to the name of the human, in order to distinguish each person, in the birth of each person has a name

(3) C language is composed of functions, a C program may have more than one function, in order to distinguish these functions, each function is given a name. The name of the function is one of the identifiers. In addition to the function, the name of the variable is also an identifier.

three. Naming

Naming rules (be sure to follow)

Can only be made up of 26 letters in uppercase and lowercase, 10 Arabic numerals 0~9, underline _

Strictly case-sensitive, such as test and test are 2 different identifiers

Cannot start with a number

You cannot use a keyword as an identifier

Naming conventions

1. Try to make a meaningful name, such as a complete English word, which can be useful if someone sees the name. If you do not understand English, you can also use pinyin, try not to be like ABCDE, SFSDFSDF and other such seemingly meaningless names

2. If the identifier contains multiple words, you can use the Hump logo (except for the first word, the first letter of each word is capitalized): FirstName, MyFirstName, or use the underscore _ to connect: first_name, My_first_name

Common identifiers are named incorrectly

Legal identifiers	Illegal identifiers	Comments
FromNo12	From#12	The # symbol cannot be used in identifiers
My_boolean	My-boolean	The "-" symbol cannot be used in identifiers, and the underscore "_" should be used instead
Obj2	2ndObj	Identifiers cannot start with numbers
MyInt	Int	"Int" is the built-in keyword
Jack_rose	Jack&rose	Symbol ' & ' cannot appear in the identifier
Gui	G.u.i	The identifier must appear inside the "." Separator

Four. Notes1. What is a comment

1) Annotations are a concept that is very important in all computer languages, literally, the meaning of annotations and explanations.

2) Comments can be used to explain the meaning of a program or a line of code to facilitate communication between programmers. If I finish writing a line of code and add the corresponding comment, then people will see this comment and know what my line of code is for.

3) Comments can be any text, which means you can write Chinese

4) Note in development tools is generally red bean paste Green

2. Single-line Comment

1) The single-line comment starts with two forward slashes, that is, starts with//, can only comment one line, from//start to the end of this line is the contents of the comment

2) anywhere you can write a comment: Outside the function, inside, behind each statement

3. Multi-line annotations

Multiline comments start with/*, end with */, the contents of/* and/* are commented

4. The role of annotations

1> Annotated code does not participate in compilation

L comments are written to people, and when the program is compiled, comments are not compiled into the. O Destination file

L from the size of the. o file can be indirectly seen that the code after the comment is not compiled

2> checking the role of code

3> Troubleshooting Errors

C-keywords, identifiers, comments